1. Field of the Invention
The invention relates to special arrangements of supports in thin strip casting plants.
2. Discussion of the Prior Art
A thin strip casting plant refers here to a plant in which the liquid steel is transported via a feeding system to a circulating belt which is cooled from below by water. The underside of the applied layer of steel then solidifies in contact with the belt and the upper side solidifies as a free surface under inert gas or, to achieve better surface properties, in contact with an upper roller. After solidifying completely, the strand (thin strip) produced leaves the circulating transport belt and is transported further by a driver. The casting thickness of the strip (about 10 mm) can be chosen largely optimally for the required thickness of the finish-rolled hot strip (1 to 3 mm) and the required hot deformation for achieving adequate material properties. The optimum casting thickness is in this case the thickness at which the required degree of hot deformation is achieved with as little deformation work as possible.
The circulating transport belt makes it possible for the strand to be cooled and supported largely without friction over a long distance. This results in a high casting rate, which is a prerequisite for a direct coupling between the casting plant and the rolling stage, and high productivity as a basic condition for the casting of ordinary steels.
The circulating belt, accessible from above and the front, makes it easier for the steel to be fed in. Unlike in other processes, the steel does not have to be guided into a narrow gap between two belts or rolls.
In the area between the conveying rollers for the circulating belt, a cooling device (water cooling with suitable nozzles) is arranged on the side of the circulating belt facing away from the steel, for cooling said belt. In spite of this cooling, the high temperatures applied to the upper side of the belt by the steel melt cause the circulating belt to curve upward. This upward curvature results in the strand also being shaped in its upper surface. To avoid the upward curvature, a negative pressure is set in the cooler. The difference in pressure causes the circulating belt to be pressed onto supports.
The supporting rollers used in the past (See Production of steel strip with a single-belt process, K.-H. Spitzer and K. Schwertfeger, ISM November 1995, page 51) exhibited in the past a longitudinal section with grooves which (FIG. 12 of the publication) had supporting rollers, that is to say a profiled surface, the profile having in a longitudinal section portions of larger diameter than the minimum roller diameter. The width of these spacings corresponded in the past substantially to the distance between the portions.
In the case of such roller designs, it was not possible for the particularly thermally induced stresses in the circulating transport belt to be reduced in a controlled manner. As soon as the stability limit is exceeded by excessive stresses, the circulating belt curves up with a particular tendency in the central area. The negative pressure which has been set thus does not lead to the desired result in the case of the roller design used in the past, since the upward curvature of the circulating belt continues to influence the shape of the strand in an undesired way.